Date of Award

5-2026

Document Type

Scholarly Project

Degree Name

Doctor of Physical Therapy (DPT)

Department

Physical Therapy

First Advisor

Gary Schindler

Abstract

The benefits of blood flow restriction (BFR) training, particularly its ability to induce muscle hypertrophy, are well established. However, the physiological mechanisms underlying this hypertrophy remain unclear. This study hypothesized that fluid shifts within the skeletal muscle, specifically changes in intracellular fluid (ICF) and extracellular fluid (ECF) composition, contribute to hypertrophic responses following BFR exercise. The purpose of this study was to investigate ICF and ECF dynamics in the lower extremity skeletal muscle using bioelectrical impedance spectroscopy (BIS) following BFR in combination with submaximal resistance exercise. Additionally, the researchers aimed to determine the duration of fluid shifts by assessing ICF/ECF ratios at 3-, 30-, and 60-minute post-exercise.

Participants were randomly selected from college-aged individuals who completed a standardized resistance training protocol targeting the dominant leg. The exercise consisted of long arc quadriceps extensions using the established BFR repetition scheme: 1 set of 30 repetitions followed by 3 sets of 15 repetitions, with 30-second rest intervals. A metronome was used to ensure consistent 2-second concentric and eccentric phases. BFR was applied only to the dominant limb, while the contralateral limb served as a control. BIS measured fluid shifts (ICF/ECF ratios) in both limbs at baseline and at 3-, 30-, and 60-minutes post-exercise.

Paired sample t-tests revealed significant differences in ICF/ECF ratios between the BFR and non-BFR limbs. Repeated measures ANOVA showed significant time-dependent changes in the BFR limb across all time points. The most substantial shift occurred at 30 minutes of post-exercise, where ECF increased markedly, suggesting it may have been the primary driver of the observed fluid shifts.

These findings align with prior MRI-based studies and indicate that BFR exercise leads to temporary, measurable shifts in muscle fluid composition. Given that ICF/ECF ratios are linked to cellular function and health, these changes may have implications for improving muscle power, endurance, and recovery. This supports the therapeutic and performance-enhancing potential of BFR in both athletic and rehabilitative settings.

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